The present invention relates to an image forming apparatus.
A conventional image forming apparatus such as a printer, a copier, a facsimile machine, a complex machine or the like is configured to form an image as follows. A charging device uniformly charges a surface of a photosensitive drum. An exposing device irradiates the surface of the photosensitive drum so as to form a latent image. Then, a developing device develops the latent image on the photosensitive drum with a toner to thereby form a toner image. The toner image is transferred to a recording medium, and is fixed to the recording medium by a fixing device.
In the developing device, a toner cartridge supplies a toner (i.e., a developer) to a developing roller and a supplying roller. The toner is electrically charged by frictional electrification at a portion between the developer roller and the supplying roller, and a portion between the developing roller and a developing blade. A toner layer having a uniform thickness is formed on a surface of the developing roller by the developing blade. Generally, an image forming apparatus of non-magnetic and single-component developing type (using a non-magnetic and single-component toner) has a configuration in which the developing roller and the photosensitive drum are disposed in contact with each other. Such an image forming apparatus has a simple and compact structure, and is broadly used.
The image forming apparatus of this type is configured to apply a predetermined charge to the toner so that the toner moves from the developing roller to the latent image on the photosensitive drum. In this regard, if an abnormally charged toner (i.e., a toner with remarkably increased or decreased electric charge) is generated, such an abnormally charged toner is likely to adhere to a non-exposed area on the photosensitive drum, and may cause an abnormal image such as fog or smear.
Therefore, there is proposed a technique for discarding the abnormally charged toner. In the technique disclosed in Japanese Laid-open Patent Publication No. 2004-45481, a predetermined latent image is formed on the surface of the photosensitive drum using the exposing device. The abnormally charged toner in the toner layer on the developing roller adheres to the latent image, and is scraped off therefrom by a cleaning device (i.e., is discarded).
In the above described conventional technique, the abnormally charged toner in the toner layer on the developing roller can be discarded. However, other abnormally charged toner existing in the interior of the developing device can not be discarded.